SYNGAMY 



233 



Bryophytes and Pteridophytes. — The cytological details of the union 

 of the motile spermatozoid with the egg in bryophytes are best known in 

 certain liverworts, owing especially to the researches of Showalter 

 (1926a6, 1927 ab, 1929). In Riccardia pinguis (Fig. 140) the elongated 

 body of the spermatozoid applies itself to the surface of the egg, becomes 

 more slender, and gradually sinks through the membrane into the cyto- 

 plasm. The chromatic matter of the egg nucleus contracts, and one end 

 of the sperm nucleus extends through the membrane of the egg nucleus, 

 where it becomes considerably swollen. The female nuclear matter then 

 loosens up, and the swollen end of the penetrating male nucleus is seen to 

 lose its definite outline and differentiate a chromatic reticulum and a 

 nucleolus. After penetration is complete the 

 female and male reticula remain distinguish- 

 able for some time, but in the late prophase 

 and the metaphase of the first embryonal 

 mitosis the chromosomes of the two parents 

 form a single group. The fate of the cyto- 

 plasm, blepharoplast, and cilia of the male 

 gamete is uncertain, but in view of what has 

 been observed in other species it is highly 

 probable that they are absorbed in the egg 

 cytoplasm. 



In a number of other liverworts^*^ the male 

 nucleus does not enter the egg nucleus in the 

 compact form but becomes vesicular and 

 reticulate in some degree before the fusion 

 occurs (Fig. 141). In Sphoerocarpos it ap- 

 pears that the nuclei do not undergo fusion while in this state but 

 develop separately their chromosomes, which then take their places in a 

 common mitotic spindle, as in many animals. In Preissia, centrosomes 

 are reported in the egg cytoplasm during the fertilization period. This, 

 together with observations on certain algae (p. 227), suggests that in 

 certain plants, as in animals, the differentiation of division centers in 

 the egg cytoplasm may be induced in some manner by the entrance of the 

 spermatozoid. The fate of the non-nuclear portions of the spermatozoid 

 may prove to be of interest in this connection. 



In the pteridophytes^^ the multiciliate spermatozoid enters the egg 

 cytoplasm. It has been stated that it continues into the egg nucleus in 

 its entirety, but in Lygodium it has been clearly shown that the cilia (and 



^^Pellia Fahbroniana (Showalter, 19276); Riccia (Garber, 1904; Black, 1913); 

 Corsinia (K. Meyer, 1911); Preissia quadrata (Graham, 1918; Haupt, 1926); Rehoulia 

 (Woodburn, 1920); Sphcerocarpos (Rickett, 1923). In Funaria flavicans (moss) the 

 male nucleus enters rounded up but still compact (Beardsley, 1931). 



" Pilularia (Campbell, 1888); Onoclea (Shaw, 18986); Nephrodium (Yamanouchi, 

 1908b); Lygodiu7n (Rogers, 1926); Equisetum (Sethi, 1928). 



Fig. 141. — Syngamy in 

 Anthoceros. Male and female 

 nuclei about to fuse in lower 

 part of egg in venter of archego- 

 nium; elongated plastid above 

 them. Gametophyte cells show 

 one nucleus and one plastid each. 



